In a large pan over medium heat add the bacon. Cook for 5 minutes until the bacon is beginning to crisp. Add the onions, garlic, 3 torn sage leaves, and the pumpkin. Saute until the onions caramelize, about 5 minutes. Pour the chicken stock into pan to deglaze and simmer until the pumpkin is completely soft, about 10 to 12 minutes. Once the pumpkin is tender, pour the gravy through fine mesh strainer, into a bowl. Press the solids with a spoon to extract all the liquid and pulp possible. Return the gravy to the pot and continue to simmer and reduce by half, about 15 minutes. Season with salt and pepper, to taste, and add the remaining 3 whole fresh sage leaves. Stir in the butter and once combined pour the gravy into a serving bowl or pitcher.